The success of any test involving fluorescence (LPI, MPI, contamination, etc.) is based on having sufficiently high UV intensity and low visible light intensity for optimum contrast. All relevant NDT Codes stipulate these values.
It should be noted that legacy Mercury vapor lamps decrease in intensity with age, use and contamination. This results in a decrease in intensity over time. We offer Radiometers (UV Meters) and Photometers (Visible Light Meters) from Spectronics, Baugh & Weedon, Gould-Bass, UV Products, Magnaflux and our Economical House Brand.